1. Field of the Invention
The present invention relates to a method for fabricating a screen in a color CRT(Cathode Ray Tube), and more particularly, to a method for fabricating a screen in a color CRT, in which, in formation of a color filter film and a fluorescent film on the same time, a pigment layer is formed, a photo sensitive resin solution is coated thereon, a fluorescent material layer is sprayed thereon, and the pigment layer and the fluorescent film are exposed and developed, to prevent the pigment layer and the fluorescent film from peeling off and to form thin and close packed fluorescent films on the photo sensitive resin solution, for enhancing a contrast and a color purity as well as a luminance and cutting characteristics.
2. Background of the Related Art
Referring to FIG. 1, the color CRT is provided with a panel 1 having a flourescent film 3 coated on an inside surface thereof, a funnel 2 welded to the panel 1 by using a welding glass having a conductive graphite coated on an inside surface thereof, an electron gun 6 mounted in a neck 4 of the funnel 2 for emission of electron beams 5, a shadow mask 7 inside of the panel 1 supported on a frame 8 for selection of a color, and a deflection yoke 9 on an outer circumference of the funnel for deflection of the electron beams in left and right directions. In the cathode ray tube, when a video signal is received at the electron gun 6, thermal electrons are emitted from a cathode in the electron gun, and travels toward the panel as the electron beams are accelerated and converged by voltages applied thereto from respective electrodes of the electron gun. In this instance, the electron beams 5 has travel paths adjusted by magnetic fields from magnets fitted in the neck of the funnel, directed onto an inside surface of the panel by the deflection yoke 9, subjected to color selection as the electron beams 5 pass through slots in the shadow mask 7, and hit the fluorescent film 3 on the inside surface of the panel, to reproduce the video signal. And, in order to prevent the electron beams from being influenced from, and deflected by the geomagnetism in a course of passing through the slot in the shadow mask, and reaching to the fluorescent film, there is an inner shield 10 fitted to a rear side of the frame when it is seen from the panel.
A related art method for fabricating a screen having a color filter film for a color group the same with a fluorescent film formed on an inside surface of a panel for enhancing a luminance and contrast will be explained with reference to FIGS. 2A.about.2I.
An inside surface of the panel 1 is cleaned by using caustic soda and hydrofluoric acid, photoresist(PAD+Azide group) is coated on the inside surface of the panel by whirler, the photoresist is dried, and red, blue and green fluorescent films are exposed on an exposer by using a high pressure mercury lamp, to radiation cure the exposed portions not for using, and developed by pure water at a fixed development pressure of 3.about.5 kgf/cm.sup.2. And, a coat of graphite is applied thereon, and dried, etched with an etching solution(H.sub.2 O.sub.2 +NH.sub.4 OH), to form a light absorbing film(a black matrix) 101 as shown in FIG. 2A, and, as disclosed in JP publication No. S64-7457, a photosensitive slurry containing a first color(such as blue) pigment is coated on the inside surface of the cathode ray tube to form a first color pigment layer as shown in FIG. 2B. The first color pigment layer is dried(FIG. 2C), and exposed by using an exposure mask, and unexposed portion of which are removed by development, to form the first color pigment layer 102B as shown in FIG. 2D. After formation of a second color(such as green) pigment layer and a third color(such as blue) pigment layer in succession in the same process as the first color pigment filter layer 102B, a fluorescent layer is formed. That is, a photo sensitive slurry containing a first color(such as blue) fluorescent material particles is coated on the pigment layer as shown in FIG. 2E, to form a first color fluorescent material layer, dried, exposed by using an exposure mask as shown in FIG. 2F, developed, and dried, to remove unexposed portions as shown in FIG. 2G, to form a first color fluorescent material layer 103B on the first pigment filter layer 102B. Then, a second color fluorescent material layer 103G and a third color fluorescent material layer 103R are formed in succession by the same process as the first fluorescent material layer forming process, to provide the pigment filter layers 102R and 102G, and a fluorescent film first layers 103R and 103G as shown in FIG. 2H, and then, a metal reflection film 104 of aluminum is formed as shown in FIG. 21.
As an alternative method(JP publication No. H4-26679) to the foregoing related art method for fabricating a screen, in which formation of the pigment layers and the fluorescent material layers are done almost on the same time, by applying a coat of photosensitive slurry containing a first color(for example, blue) to the inside surface of the panel to form a first color pigment layer, applying a coat of photosensitive slurry containing the first color(for example, blue) fluorescent material particles to the first color pigment layer to form a first color fluorescent material layer, exposing and developing the first color pigment layer and the first color fluorescent material layer on the same time by using an exposure mask, to remove unexposed portions to form a first color pigment layer and fluorescent material layer at a position corresponding to the first color. Then, by using the same process, a second color layer(green) and a second fluorescent material layer, and a third color layer(red) and a third fluorescent material layer are formed in succession.
Because the method disclosed in JP publication No. S64-7457 requires coating, exposure, and development for a photosensitive slurry containing a pigment or a fluorescent material for three color pigments and three color fluorescent material, the method requires two times of steps compared to a case when fluorescent material patterns of fluorescent material having pigment attached thereto, that increases the fabrication cost. And, because the method disclosed in JP publication No. H4-26679 omits exposure and development for the blue, green, and red pigment layers respectively, though the method disclosed in JP publication No. H4-26679 is advantageous in that a production cost is saved since the method disclosed in JP publication No. H4-26679 has less fabrication steps, the omission of the exposure and development of the pigment layer is not favorable for formation of a high quality fluorescent material surface. That is, as the photosensitive slurry in formation of the pigment layer, though a mixed solution of polyvinylalcohol as a photosensitive agent and bichromate as a photo cross linking agent is in general used, if the fluorescent material slurry is coated on an unexposed or undeveloped pigment layer as disclosed in JP publication No. H4-26679, photosensitive components contained in the pigment layer, particularly the bichromate as the photo cross linking agent, start to be dissolved in water contained in the alkali slurry since the bichromate is a material dissolved in water well. As a result of this, when the pigment layer and the fluorescent material layer are exposed, the exposed portion is not cured adequately due to lack of the photo cross linking agent in the pigment layer. And, the fluorescent material layer with a 20.about.30 .mu.m thickness before the exposure is too thick to be photo cured adequately when the filter layer and the fluorescent material layer are exposed on the same time. That is, the inadequate cure of the pigment layer leads the pigment layer and the fluorescent material layer susceptible to peeling in development of the pigment layer and the fluorescent material layer after exposure, that impedes formation of a high quality fluorescent material surface.